1. Field of the Invention
The present invention relates to a separation membrane module provided with a large number of hollow fibers, and in particular to a separation membrane module having hollow fibers that is used for the purpose of gas separation, degassing, dissolution of gases in liquids, and the like, and that has a large number of hollow fibers in which a thermofusible synthetic resin is provided at least on the surfaces thereof; and to a manufacturing method thereof.
2. Description of Related Art
Separation membrane modules that use hollow fibers have an increased membrane surface area per unit volume, and are therefore used as modules having a large number of porous separation membranes in the form of hollow fibers.
The vacant spaces between the hollow-fiber separation membranes, and the voids between the hollow-fiber separation membranes and the outer cylinder for housing these membranes, are sealed by a sealant or the like at both ends of the large number of hollow-fiber separation membranes in a separation membrane module having hollow fibers to guaranteed airtightness.
The method whereby a low-viscosity resin, such as epoxy resin, urethane resin, or silicone resin, is injected into the ends as a sealant and caused to thoroughly fill the voids by being left at rest subjected to centrifugal force, and then cured by heating, is known as a method of sealing the voids between the outer cylinder and hollow fiber bundles, and between the hollow fiber bundles themselves.
However, the sealant resins are inadequate in terms of heat resistance and chemical resistance. Therefore, their use is limited to applications in which acid- or alkali-containing solutions or organic solvents are used as the media or liquid detergents, or to applications in which steam sterilization is performed.
On the other hand, when a thermofusible resin is used as a sealant for hollow fibers, it is difficult to penetrate fine voids, such as those between the outer cylinder and hollow fiber bundles or between the hollow fiber bundles, if the viscosity of the thermofusible resin is high. Moreover, it is difficult to defoam high-viscosity resins once air bubbles have formed, and inadequate sealing sometimes results.
Methods have also been proposed in which an outer cylinder with through-holes in the form of a beehive (that is, a honeycomb) is preformed from a resin, and hollow fibers are then inserted into the through-holes and melted by heat, but it is difficult in itself to form a large number of through-holes at a high density in the outer cylinder, and it is difficult to completely seal the voids. Consequently, it is impossible to finely mold sealed parts using a thermofusible resin, and neither is it possible to raise the hollow fiber packing rate by these methods.
Moreover, Japanese Kokai Patent No. 4-354521 proposes a method of manufacturing a hollow-fiber porous separation membrane element whereby a thermofusible resin that has been melt-molded into a predetermined shape is inserted into one end of an outer cylinder, and while this thermofusible resin is heated and melted, bundles of hollow-fiber porous separation membranes made from fluororesin are inserted from the other end of the outer cylinder and embedded in the thermofusible resin by gravity, loading, attraction, or a combination of these to form a sealed end part from the thermofusible resin. However, it is necessary to use porous polytetrafluoroethylene for the hollow fibers, and to provide a separate sealing material.
These and other purposes of the present invention will become evident from review of the following specification.